This application claims the priority of German Patent Document DE 101 58 873.9, filed on Nov. 30, 2001, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a hydraulic valve control arrangement with a control line of a control cylinder, said control line being connected to a first oil volume, with a first control piston having a control face A1 and operatively connected to the first oil volume, and with a plunger piston which is arranged between the first control piston and an outlet valve and has a control face A2 and which is operatively connected to a second oil volume.
A hydraulic valve control is already known from German Patent Document DE 195 42 561 C1, having preferably two pistons which are separated from one another and act selectively on the valve and which are connected to a high-pressure accumulator. In this case, the piston arrangement is capable of being acted upon by fuel maintained at a different pressure level, and, at the end of the opening operation and during the closing operation, the moved mass can be reduced. To open the valve, the piston arrangement is acted upon by fuel of higher pressure and, for closing, is acted upon by fuel of lower pressure. Two different pressure levels of the pressure accumulator or pressure accumulators are therefore necessary.
In particular British Patent Document GB 2 265 419 A describes a piston arrangement of a compression brake, having a telescopically connected piston arrangement in which a first volume delimited via a plunger piston bearing against a rocker is acted upon by excess pressure. In this case, an actuating force of the actual displacement piston is generated counter to the closing force of the valves, the actuating force ultimately resulting in the opening of the valves. The piston arrangement is integrated at any time into the force flux of the rocker. There is no provision for a gradation of the actuating force.
An aspect of certain preferred embodiments of the invention is to design and arrange a hydraulic valve control device in such a way that different actuating forces are ensured by way of one pressure level.
This aspect can be achieved, according to certain preferred embodiments of the invention, in that a first control edge, switching the first throughflow connection from the first oil volume to the second oil volume operatively connected to a control face A3 of the first control piston, is provided between the control cylinder and the first control piston. Thereby the second oil volume is cut in by the control edge after a defined displacement S1 of the control piston and a counterforce F3 to the current actuating force F1 is generated according to the arrangement of the control face A1 and control face A2 or according to their face ratio. Thus, during the second part of the valve stroke, the valve-opening force decreases according to the control-face ratios, and increased wear on the materials and also an overshoot of the outlet valve are avoided.
For this purpose, it is advantageous that, starting from a neutral position of the first control piston, the first throughflow connection is opened after a displacement S1 of the first control piston or of the first control edge. It is therefore unimportant whether the control edge or the control piston executes the displacement S1 so that the throughflow connection is opened.
Furthermore, it is advantageous that the control face A3 is arranged opposite the control face A1 and the control face A2, opposite control faces being acted upon by oil pressure generating opposed actuating forces. Thus, the control face A3 generates an actuating force opposed to the control face A1 and control face A3.
Moreover, a solution is achieved in that a first control edge switching the first throughflow connection from the first oil volume to the control face A1 of the first control piston is provided between the control cylinder and the first control piston or a second control piston. Thereby the control face A1 is cut in by the first control edge after an initial displacement S0. The cut-in control face A1 also generates a corresponding control force F1 which then assists the operation of opening the outlet valve.
For this purpose, it is advantageous that the first control piston or a second control piston has a control face A0, which is operatively connected to the first oil volume during the displacement S0, and the first control edge closing the first oil volume. Consequently, the oil volume is closed with respect to the control face A1 during the displacement S0 and is throughflow-connected to the smaller control face A0. Accordingly, only a control force F0 corresponding to the control face A0 is generated over the initial displacement S0 and is then increased to F1 by the operation of opening the control face A1.
It is also advantageous, for this purpose that, after the displacement S0, the first control edge is in a position opening the first oil volume, a first throughflow connection from the first oil volume to the control face A1 being provided after the displacement S0. After the displacement S0, the control face A1 is acted upon by oil pressure by the first throughflow connection, so that, from this point in time, an increased control force F1 is available.
Finally, according to a preferred embodiment, there is provision for a second throughflow connection designed as a throttle to be provided between the first oil volume and the control face A1. Thus, even before the end of the displacement S0, an oil pressure is exerted on the control face A1, so that, in this position, an actuating force arises via the control face A1 according to the throttle cross section or to the prevailing oil pressure.
It is particularly advantageous that the displacement S0 corresponds to a valve clearance and the displacement S1 corresponds to an opening displacement of the outlet valve, the opening displacement being between 5% and 50%, in particular between 10% and 20%, of the total valve displacement SG, and the displacement S2 constituting a displacement which completes the total valve displacement SG. By virtue of the existing pressure-space conditions or of the valve-actuating device, an optimum distribution of the actuating force to the outlet valve can be ensured. The valve-clearance compensating stroke requires a low actuating force, and the first part of the opening stroke of the outlet valve requires the highest actuating force, since the outlet valve has to be opened counter to the highly compressed combustion-space gases. After opening, and over the last part of the opening stroke, a low actuating force is again required, since, at this point in time, the combustion space is already depressurized.
In connection with the design and arrangement according to certain preferred embodiments of the invention, it is advantageous that, after the displacement S1, the control face A0 is operatively connected to the first oil volume, and a second control edge closing the first oil volume via the displacement S2 is provided. This ensures a reduction of the effective control face A1 to the control face A0, so that the completion stroke S2 is executed with a lower actuating force.
It is advantageous, furthermore, that the first control piston or the second control piston has the first control edge and/or the second control edge, after the displacement S0 the first control edge being operatively connected to a first control groove of the control cylinder, and after the displacement S2 the second control edge being operatively connected to a second control groove of the control cylinder. The control piston can therefore have a one-part or two-part design, the necessary control edges and the control grooves which correspond to them being provided, within the control-piston wall, on the second or on the one control piston.
Moreover, it is advantageous that the second control piston is arranged upstream of the first control piston in the displacement direction and/or the first control piston has a first return element, such as a spring, which acts counter to the actuating force F1 and which generates a return force Fxc3x9c. The control piston is returned into the initial position after the opening stroke by way of the spring.
Furthermore, it is advantageous that the face ratios A1/A2 and A1/A0 are between two and ten, in particular between three and five, and the control face A1 is equal to the control face A3. The force ratio of the individual opening displacements is defined by the face ratios.
Consequently, in addition, the transmission ratio of the two control pistons is also defined during the displacement S2, since, in the case of a constant oil volume flow (dV/sec), the displacement (ds) of the second control piston is directly proportional to its piston cross-sectional area. While the second control piston is moving by the amount of ds2=dV/A0, the first control piston can move only by the amount ds1=dV/A1 (A1 greater than A0xe2x86x92ds2 less than ds1), since the oil volume between the two pistons is closed. However, since the second control piston bears against the first control piston, a vacuum arises in the second oil volume.
Finally, it is advantageous that the first oil volume and the control face A1 of the first control piston are acted upon by oil pressure via the control line, a control force F1 is generated and the first control piston is set in displacement motion, at the same time, the plunger piston, which bears against the first control piston, and the outlet valve being set in motion counter to the valve-spring force FV. After the displacement S1 of the first control piston, the first throughflow connection to the second oil volume is opened via the first control edge, the outlet valve being opened by the amount of the displacement S1 via the plunger piston by way of the first control piston. The control face A3 is acted upon by oil pressure via the second oil volume and a counterforce F3 to the control force F1 is generated, and an additional return force FU to the counterforce F3 is generated by way of the first return element, at the same time, the control face A2 of the plunger piston being acted upon by oil pressure and a completing control force F2 of the plunger piston being generated. By way of the resulting control force FR=F1+F2xe2x88x92F3 (xe2x88x92FU), the outlet valve is opened completely, FRxe2x89xa7F2 being applicable in this case.
Finally, within the framework of certain preferred embodiments, it is advantageous that, in the neutral position, first the control face A0 and the first oil volume of the first control piston are acted upon by oil pressure via the control line, a control force F0 being generated and the first control piston being set in displacement motion. After a displacement S0 of the first control piston, the first throughflow connection from the first oil volume to the control face A1 is opened via the first control edge, and the control force F1 is generated, in the neutral position, the control face A1 being acted upon by oil pressure, starting from the first oil volume, via the throttle-like second throughflow connection. After a displacement S1, the first oil volume is closed by the second control edge and the control face A1 is partitioned off, and, consequently, the first oil volume and the control face A0 are then acted upon by oil pressure via the control line, and the control force F0 is generated. By way of the resulting control force FR=F0xe2x88x92FU, the outlet valve is opened completely, F0xe2x89xa7FU being applicable in this case.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.